The invention relates generally to digital loop carrier systems in telecommunications networks, and in particular, to enhanced call handling for distribution resource errors in digital loop carrier systems.
When a calling party places a telephone call, a request for a telephone call connection to a called party is submitted over a telephone network. A telecommunications switch terminating the called party receives this request and determines which telephone line and associated customer premise equipment the telephone call connection is intended for. The telecommunications switch then checks whether the line is free for a telephone connection. If the line is available, the telecommunications switch establishes a telephone connection to the customer premise equipment. If the line and customer premise equipment are not available, the telecommunications switch returns a busy signal to the calling party indicating that the customer premise equipment is currently in use or unavailable. As an alternative to the busy signal, the telecommunications switch terminates the telephone call connection, request and applies terminating call features associated with the line such as voice mail and call forwarding. The terminating call features enhance call handling for the unsuccessful calling party.
Digital loop carrier systems are known. Generally, in digital loop carrier systems, a digital loop carrier is inserted between the telecommunications switch and customer premise equipment to increase the efficiency of the resources used for the telephone network. In particular, not all customer premise equipment connected to a telecommunications switch is used at the same time. Therefore, only a percentage of the direct connections between the telecommunications switch and the customer premise equipment are necessary at any given time. A digital loop carrier attached to the telecommunications. switch exploits this by cycling limited resources to the connected customer premise equipment only when telephone service is required, which reduces the amount of fixed lines needed for telephone connections.
The digital loop carrier is connected to the telecommunications switch via a trunk connection, such as a DSl connection. The digital loop carrier is connected to the customer premise equipment via distribution resources such as optical networking units (ONU), integrated access devices (IAD), trunks, and/or fiber optic and copper lines. The digital loop carrier communicates with the telecommunications switch via a standard protocol, such as the Telcordia Publication GR-303-CORE subset of the Q. 931 International Telecommunications Union messaging standard (xe2x80x9cGR-303xe2x80x9d). According to the GR-303 standard, the messages, which include cause codes, are communicated between the digital loop carrier and the telecommunications switch for establishing telephone calls.
A successful call to a customer premise equipment terminated by a digital loop carrier connected to a telecommunications switch begins with the telecommunications switch receiving a telephone connection request to the line associated with the customer premise equipment. The telecommunications switch checks its internal status of the desired line to the customer premise equipment to determine if the line is available. If the line is available, the telecommunications switch then sends a xe2x80x9csetupxe2x80x9d message to the digital loop carrier specifying which path to receive the telephone call. If there are sufficient resources from the digital loop carrier to the desired line and customer premise equipment, the digital loop carrier sends a xe2x80x9cconnect to the digital loop carrierxe2x80x9d message to the telecommunications switch. The telecommunications switch then uses the path to ring and establish a telephone connection with the customer premise equipment.
An unsuccessful call to a customer premise equipment terminated by a digital loop carrier connected to a telecommunications switch begins with the telecommunications switch receiving a telephone connection request to the customer premise equipment. As before, the telecommunications switch checks its internal status of the desired line to the customer premise equipment to determine if the line is available. If the internal status of the telecommunications switch indicates the desired line is available, the telecommunications switch then sends a xe2x80x9csetup messagexe2x80x9d to the digital loop carrier specifying which path to receive the telephone call. The digital loop carrier then determines, in response to the xe2x80x9csetupxe2x80x9d message whether there are sufficient available resources to the desired customer premise equipment. If the digital loop carrier has a problem connecting to the customer premise equipment, for example due to a lack of resources or a fault, then the digital loop carrier rejects the xe2x80x9csetup messagexe2x80x9d by sending a xe2x80x9creject messagexe2x80x9d indicating a temporary failure without further explanation. This results in a xe2x80x9cfast busyxe2x80x9d or reorder signal being transmitted to the calling party by the telecommunications switch. Unfortunately, the telecommunications switch does not apply terminating call features, such as voice mail or call forwarding, after determining the line is available and sending the xe2x80x9csetupxe2x80x9d message. This is because, at least with regard to the switch""s view of the line, the line is available for a call. In addition, the temporary failure in the xe2x80x9crejectxe2x80x9d message is ambiguous and does not cause the telecommunications switch to apply terminating call features. The return of a reorder signal to the calling party where there is a lack of resources or fault between the digital loop carrier and the customer premise equipment is undesirable because the calling party must reinitiate the call rather than leaving a message or being forwarded to another line.
Therefore, a need exists for a system that applies terminating call features when an error occurs in the distribution resources or in the customer premise equipment terminated by a digital loop carrier.
In accordance with one aspect of the present invention a method is provided for call establishment to a customer premise equipment. The customer premise equipment is connected to a digital loop carrier via distribution resources. The digital loop carrier is connected to a telecommunications switch. The method is initiated upon the receipt of a request for a telephone call to the customer premise equipment made by the telecommunications switch to the digital loop carrier. After the request for a telephone call is received by the digital loop carrier, a determination is made as to whether the customer premise equipment is available. If the custom premise equipment is not available, for example, due to the unavailability of a distribution resource an error occurring in the distribution resources, or an error in the customer premise equipment, the digital loop carrier generates and transmits a distribution resource error message indicating the error. The telecommunications switch preferably receives the distribution resource error message and applies terminating call features for the customer premise equipment. The terminating call features include, for example, call forwarding and voice mail
In another aspect of the present invention, a telecommunications system is provided. The telecommunications system includes a telecommunications switch coupled to a digital loop carrier. The digital loop carrier couples to customer premise equipment for the transmission of telephone calls. In response to a request from the telecommunications switch to place a telephone call to the customer premise equipment that is coupled to the digital loop carrier, the digital loop carrier determines whether a telephone connection may be established between the digital loop carrier and the customer premise equipment. If a call cannot be established between the digital loop carrier and the customer premise equipment, for example, due to a lack of distribution resources, then the digital loop carrier returns a distribution resource error to the telecommunications switch. Preferably, the telecommunications switch applies a terminating call feature.